The invention relates to an optical arrangement, and more particularly, to a laser diode arrangement with at least one row of emitter elements which emit laser light and which are arranged in the row with their active layer in a common plane and perpendicular to their first axis.
The radiation of a semiconductor diode laser (here, in simplified terms, also a diode laser) is characterized by a highly diverging beam, in contrast to conventional laser beam sources, with a laser beam which has a diameter of a few millimeters with low beam divergence in the range of a few mrad, while the divergence for a diode laser exceeds 1000 mrad.
Furthermore, it is also known that in diode lasers, the angle of divergence in the plane perpendicular to the active layer, i.e. in the so-called xe2x80x9cfast axisxe2x80x9d, is greater than in the plane of the active layer, i.e. in the so-called xe2x80x9cslow axisxe2x80x9d.
To attain a laser power as high as possible, for example 20-40 watts from a semiconductor chip, numerous emitters are combined on a so-called bar. Ordinarily 10-50 individual emitters, or emitter groups, are arranged following one another in a row in the plane parallel to the active layer, i.e. in the slow axis. The resulting overall beam of this bar in the plane parallel to the active layer has an opening angle of roughly 10xc2x0 and a beam diameter of roughly 10 mm. This yields a beam quality in this plane which is many times less than the beam quality in the plane perpendicular to the active layer.
The occupation density which results from the quotient of the radiating area of the laser bar to the total area in currently available diode laser bars is roughly 30-50%, in any case higher occupation densities allowing only pulsed operation of the laser. For continuous applications, smaller occupation densities are necessary.
In order the make the highly divergent radiation of a diode laser useful for laser applications, for example, material machining, medical technology, pumping of solid state lasers, etc., collimating and focusing optical arrangements are necessary in the beam path. These optical arrangements contain one fast axis collimator, which is made as micro optics, and which has the optical property of a cylinder lens which lies with its axis parallel to the slow axis, for all emitters of a diode laser bar its own continuous cylinder lens being used with a small focal distance in the immediate vicinity of the facet of the diode laser bar, i.e. at a distance of a few hundred mu from the emitters or from this facet. The divergence in the slow axis is then corrected by following macro-optics.
To attain higher powers, as are necessary, for example, in materials machining, in medical engineering, for pumping of solid state lasers, etc., providing several rows of emitters or several diode laser bars in a stack in several planes on top of one another is known, these planes being offset against one another in the direction of the fast axis and to each row of emitters, or each diode laser bar of each plane, its own fast axis collimator being assigned.
In particular, a laser diode arrangement (U.S. Pat. No. 5,802,092) is known in which the slow axis collimator is formed by a host of cylinder lens elements which follow one another in the direction of the slow axis and which with their axes are each located in the fast axis and of which one element at a time is assigned to one emitter of a row of emitters. Furthermore, the arrangement is made such that the beams of the individual emitters which are collimated in the plane of the slow axis with the cylinder lens elements, which are parallel, or essentially parallel, directly adjoin one another so that a beam cluster with a high filling factor is achieved which then can be focussed using a focussing lens at the focal point.
However, optimum focusing of the radiation of all emitters at a common focus requires optimum fast axis collimation and with it alignment of the individual beams of the emitters of the respective row, or respective bar, as parallel as possible, such that the emitters could be imaged on a line as straight as possible after this fast axis collimation. But generally, this cannot be accomplished in ideal form, due to nonconformities, i.e. deviations of the conformity between the diode laser bars and the fast axis collimator. These deviations can be of different origin, for example due to production tolerances and/or deformation during installation, etc. These nonconformities which are not avoided in the prior art, lead to widening of the focus in the fast axis and thus to degradation of the beam quality at the focus.
The object of the invention is to devise an optical arrangement and a laser diode arrangement with one such optical arrangement which avoids these defects.
By dividing at least the part of the correction optics of at least one row of emitter elements, i.e. the part acting as the fast axis collimator, into several segments, the degradation of beam quality at the focus, especially the widening of the focus, which is caused by the nonconformities between the diode laser bars, or between the row of emitter elements, and the correction optics, can be effectively prevented.
According to another aspect, the invention relates to i a special execution of the correction optics such that it is formed by at least one lens element, but preferably by several lens elements which adjoin one another in the direction of the slow axis, which acts, or act, both as the fast axis collimator and as the slow axis collimator, both effects being accomplished in a single lens body of the respective lens element. However, each lens element can also be built of several lenses following one another in the beam path. If the lens elements each consist of only a single lens body, there is also the possibility of producing all the correction optics, or just segments of these optics, in one piece or monolithically.